X-Git-Url: http://plrg.eecs.uci.edu/git/?p=model-checker.git;a=blobdiff_plain;f=model.cc;h=73bafc004b6cf50d3dc94b940d3dc4005a68b93b;hp=6453d537a93fdb41b91fa995551611e61f69c2fa;hb=ee296f053997ba5914f29334960dade61b1654e3;hpb=d2985e8129a69c7fb28c080272988485830c2bd9 diff --git a/model.cc b/model.cc index 6453d53..73bafc0 100644 --- a/model.cc +++ b/model.cc @@ -39,7 +39,6 @@ struct bug_message { */ struct model_snapshot_members { model_snapshot_members() : - current_action(NULL), /* First thread created will have id INITIAL_THREAD_ID */ next_thread_id(INITIAL_THREAD_ID), used_sequence_numbers(0), @@ -48,6 +47,7 @@ struct model_snapshot_members { stats(), failed_promise(false), too_many_reads(false), + no_valid_reads(false), bad_synchronization(false), asserted(false) { } @@ -58,7 +58,6 @@ struct model_snapshot_members { bugs.clear(); } - ModelAction *current_action; unsigned int next_thread_id; modelclock_t used_sequence_numbers; ModelAction *next_backtrack; @@ -66,6 +65,7 @@ struct model_snapshot_members { struct execution_stats stats; bool failed_promise; bool too_many_reads; + bool no_valid_reads; /** @brief Incorrectly-ordered synchronization was made */ bool bad_synchronization; bool asserted; @@ -159,6 +159,14 @@ void ModelChecker::reset_to_initial_state() /* Print all model-checker output before rollback */ fflush(model_out); + /** + * FIXME: if we utilize partial rollback, we will need to free only + * those pending actions which were NOT pending before the rollback + * point + */ + for (unsigned int i = 0; i < get_num_threads(); i++) + delete get_thread(int_to_id(i))->get_pending(); + snapshot_backtrack_before(0); } @@ -203,11 +211,14 @@ Node * ModelChecker::get_curr_node() const * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be * followed by a THREAD_START, or it can enforce execution replay/backtracking. * The model-checker may have no preference regarding the next thread (i.e., - * when exploring a new execution ordering), in which case this will return - * NULL. - * @param curr The current ModelAction. This action might guide the choice of - * next thread. - * @return The next thread to run. If the model-checker has no preference, NULL. + * when exploring a new execution ordering), in which case we defer to the + * scheduler. + * + * @param curr Optional: The current ModelAction. Only used if non-NULL and it + * might guide the choice of next thread (i.e., THREAD_CREATE should be + * followed by THREAD_START, or ATOMIC_RMWR followed by ATOMIC_{RMW,RMWC}) + * @return The next chosen thread to run, if any exist. Or else if no threads + * remain to be executed, return NULL. */ Thread * ModelChecker::get_next_thread(ModelAction *curr) { @@ -216,14 +227,17 @@ Thread * ModelChecker::get_next_thread(ModelAction *curr) if (curr != NULL) { /* Do not split atomic actions. */ if (curr->is_rmwr()) - return thread_current(); + return get_thread(curr); else if (curr->get_type() == THREAD_CREATE) return curr->get_thread_operand(); } - /* Have we completed exploring the preselected path? */ + /* + * Have we completed exploring the preselected path? Then let the + * scheduler decide + */ if (diverge == NULL) - return NULL; + return scheduler->select_next_thread(); /* Else, we are trying to replay an execution */ ModelAction *next = node_stack->get_next()->get_action(); @@ -245,7 +259,7 @@ Thread * ModelChecker::get_next_thread(ModelAction *curr) /* The next node will try to satisfy a different set of promises. */ tid = next->get_tid(); node_stack->pop_restofstack(2); - } else if (nextnode->increment_read_from()) { + } else if (nextnode->increment_read_from_past()) { /* The next node will read from a different value. */ tid = next->get_tid(); node_stack->pop_restofstack(2); @@ -268,6 +282,8 @@ Thread * ModelChecker::get_next_thread(ModelAction *curr) earliest_diverge = prevnode->get_action(); } } + /* Start the round robin scheduler from this thread id */ + scheduler->set_scheduler_thread(tid); /* The correct sleep set is in the parent node. */ execute_sleep_set(); @@ -293,24 +309,47 @@ void ModelChecker::execute_sleep_set() for (unsigned int i = 0; i < get_num_threads(); i++) { thread_id_t tid = int_to_id(i); Thread *thr = get_thread(tid); - if (scheduler->is_sleep_set(thr) && thr->get_pending() == NULL) { - thr->set_state(THREAD_RUNNING); - scheduler->next_thread(thr); - Thread::swap(&system_context, thr); - priv->current_action->set_sleep_flag(); - thr->set_pending(priv->current_action); + if (scheduler->is_sleep_set(thr) && thr->get_pending()) { + thr->get_pending()->set_sleep_flag(); } } } +/** + * @brief Should the current action wake up a given thread? + * + * @param curr The current action + * @param thread The thread that we might wake up + * @return True, if we should wake up the sleeping thread; false otherwise + */ +bool ModelChecker::should_wake_up(const ModelAction *curr, const Thread *thread) const +{ + const ModelAction *asleep = thread->get_pending(); + /* Don't allow partial RMW to wake anyone up */ + if (curr->is_rmwr()) + return false; + /* Synchronizing actions may have been backtracked */ + if (asleep->could_synchronize_with(curr)) + return true; + /* All acquire/release fences and fence-acquire/store-release */ + if (asleep->is_fence() && asleep->is_acquire() && curr->is_release()) + return true; + /* Fence-release + store can awake load-acquire on the same location */ + if (asleep->is_read() && asleep->is_acquire() && curr->same_var(asleep) && curr->is_write()) { + ModelAction *fence_release = get_last_fence_release(curr->get_tid()); + if (fence_release && *(get_last_action(thread->get_id())) < *fence_release) + return true; + } + return false; +} + void ModelChecker::wake_up_sleeping_actions(ModelAction *curr) { for (unsigned int i = 0; i < get_num_threads(); i++) { Thread *thr = get_thread(int_to_id(i)); if (scheduler->is_sleep_set(thr)) { - ModelAction *pending_act = thr->get_pending(); - if ((!curr->is_rmwr()) && pending_act->could_synchronize_with(curr)) - //Remove this thread from sleep set + if (should_wake_up(curr, thr)) + /* Remove this thread from sleep set */ scheduler->remove_sleep(thr); } } @@ -323,11 +362,22 @@ void ModelChecker::set_bad_synchronization() priv->bad_synchronization = true; } +/** + * Check whether the current trace has triggered an assertion which should halt + * its execution. + * + * @return True, if the execution should be aborted; false otherwise + */ bool ModelChecker::has_asserted() const { return priv->asserted; } +/** + * Trigger a trace assertion which should cause this execution to be halted. + * This can be due to a detected bug or due to an infeasibility that should + * halt ASAP. + */ void ModelChecker::set_assert() { priv->asserted = true; @@ -524,25 +574,118 @@ bool ModelChecker::next_execution() return true; } -ModelAction * ModelChecker::get_last_conflict(ModelAction *act) +/** + * @brief Find the last fence-related backtracking conflict for a ModelAction + * + * This function performs the search for the most recent conflicting action + * against which we should perform backtracking, as affected by fence + * operations. This includes pairs of potentially-synchronizing actions which + * occur due to fence-acquire or fence-release, and hence should be explored in + * the opposite execution order. + * + * @param act The current action + * @return The most recent action which conflicts with act due to fences + */ +ModelAction * ModelChecker::get_last_fence_conflict(ModelAction *act) const +{ + /* Only perform release/acquire fence backtracking for stores */ + if (!act->is_write()) + return NULL; + + /* Find a fence-release (or, act is a release) */ + ModelAction *last_release; + if (act->is_release()) + last_release = act; + else + last_release = get_last_fence_release(act->get_tid()); + if (!last_release) + return NULL; + + /* Skip past the release */ + action_list_t *list = action_trace; + action_list_t::reverse_iterator rit; + for (rit = list->rbegin(); rit != list->rend(); rit++) + if (*rit == last_release) + break; + ASSERT(rit != list->rend()); + + /* Find a prior: + * load-acquire + * or + * load --sb-> fence-acquire */ + std::vector< ModelAction *, ModelAlloc > acquire_fences(get_num_threads(), NULL); + std::vector< ModelAction *, ModelAlloc > prior_loads(get_num_threads(), NULL); + bool found_acquire_fences = false; + for ( ; rit != list->rend(); rit++) { + ModelAction *prev = *rit; + if (act->same_thread(prev)) + continue; + + int tid = id_to_int(prev->get_tid()); + + if (prev->is_read() && act->same_var(prev)) { + if (prev->is_acquire()) { + /* Found most recent load-acquire, don't need + * to search for more fences */ + if (!found_acquire_fences) + return NULL; + } else { + prior_loads[tid] = prev; + } + } + if (prev->is_acquire() && prev->is_fence() && !acquire_fences[tid]) { + found_acquire_fences = true; + acquire_fences[tid] = prev; + } + } + + ModelAction *latest_backtrack = NULL; + for (unsigned int i = 0; i < acquire_fences.size(); i++) + if (acquire_fences[i] && prior_loads[i]) + if (!latest_backtrack || *latest_backtrack < *acquire_fences[i]) + latest_backtrack = acquire_fences[i]; + return latest_backtrack; +} + +/** + * @brief Find the last backtracking conflict for a ModelAction + * + * This function performs the search for the most recent conflicting action + * against which we should perform backtracking. This primary includes pairs of + * synchronizing actions which should be explored in the opposite execution + * order. + * + * @param act The current action + * @return The most recent action which conflicts with act + */ +ModelAction * ModelChecker::get_last_conflict(ModelAction *act) const { switch (act->get_type()) { - case ATOMIC_FENCE: + /* case ATOMIC_FENCE: fences don't directly cause backtracking */ case ATOMIC_READ: case ATOMIC_WRITE: case ATOMIC_RMW: { - /* Optimization: relaxed operations don't need backtracking */ - if (act->is_relaxed()) - return NULL; + ModelAction *ret = NULL; + /* linear search: from most recent to oldest */ action_list_t *list = get_safe_ptr_action(obj_map, act->get_location()); action_list_t::reverse_iterator rit; for (rit = list->rbegin(); rit != list->rend(); rit++) { ModelAction *prev = *rit; - if (prev->could_synchronize_with(act)) - return prev; + if (prev->could_synchronize_with(act)) { + ret = prev; + break; + } } - break; + + ModelAction *ret2 = get_last_fence_conflict(act); + if (!ret2) + return ret; + if (!ret) + return ret2; + if (*ret < *ret2) + return ret2; + return ret; } case ATOMIC_LOCK: case ATOMIC_TRYLOCK: { @@ -699,47 +842,46 @@ ModelAction * ModelChecker::get_next_backtrack() } /** - * Processes a read or rmw model action. + * Processes a read model action. * @param curr is the read model action to process. - * @param second_part_of_rmw is boolean that is true is this is the second action of a rmw. * @return True if processing this read updates the mo_graph. */ -bool ModelChecker::process_read(ModelAction *curr, bool second_part_of_rmw) +bool ModelChecker::process_read(ModelAction *curr) { + Node *node = curr->get_node(); uint64_t value = VALUE_NONE; bool updated = false; while (true) { - const ModelAction *reads_from = curr->get_node()->get_read_from(); - if (reads_from != NULL) { + const ModelAction *rf = node->get_read_from_past(); + if (rf != NULL) { mo_graph->startChanges(); - value = reads_from->get_value(); - bool r_status = false; - - if (!second_part_of_rmw) { - check_recency(curr, reads_from); - r_status = r_modification_order(curr, reads_from); - } + value = rf->get_value(); + check_recency(curr, rf); + bool r_status = r_modification_order(curr, rf); - if (!second_part_of_rmw && is_infeasible() && (curr->get_node()->increment_read_from() || curr->get_node()->increment_future_value())) { + if (is_infeasible() && (node->increment_read_from_past() || node->increment_future_value())) { mo_graph->rollbackChanges(); priv->too_many_reads = false; continue; } - read_from(curr, reads_from); + read_from(curr, rf); mo_graph->commitChanges(); - mo_check_promises(curr->get_tid(), reads_from, NULL); + mo_check_promises(curr, true); updated |= r_status; - } else if (!second_part_of_rmw) { + } else { /* Read from future value */ - struct future_value fv = curr->get_node()->get_future_value(); + struct future_value fv = node->get_future_value(); + Promise *promise = new Promise(curr, fv); value = fv.value; - curr->set_value(fv.value); - curr->set_read_from(NULL); - promises->push_back(new Promise(curr, fv)); + curr->set_read_from_promise(promise); + promises->push_back(promise); + mo_graph->startChanges(); + updated = r_modification_order(curr, promise); + mo_graph->commitChanges(); } get_thread(curr)->set_return_value(value); return updated; @@ -893,7 +1035,7 @@ bool ModelChecker::process_write(ModelAction *curr) } mo_graph->commitChanges(); - mo_check_promises(curr->get_tid(), curr, NULL); + mo_check_promises(curr, false); get_thread(curr)->set_return_value(VALUE_NONE); return updated_mod_order || updated_promises; @@ -966,7 +1108,10 @@ bool ModelChecker::process_thread_action(ModelAction *curr) switch (curr->get_type()) { case THREAD_CREATE: { - Thread *th = curr->get_thread_operand(); + thrd_t *thrd = (thrd_t *)curr->get_location(); + struct thread_params *params = (struct thread_params *)curr->get_value(); + Thread *th = new Thread(thrd, params->func, params->arg, get_thread(curr)); + add_thread(th); th->set_creation(curr); /* Promises can be satisfied by children */ for (unsigned int i = 0; i < promises->size(); i++) { @@ -1179,6 +1324,30 @@ bool ModelChecker::read_from(ModelAction *act, const ModelAction *rf) return false; } +/** + * Check promises and eliminate potentially-satisfying threads when a thread is + * blocked (e.g., join, lock). A thread which is waiting on another thread can + * no longer satisfy a promise generated from that thread. + * + * @param blocker The thread on which a thread is waiting + * @param waiting The waiting thread + */ +void ModelChecker::thread_blocking_check_promises(Thread *blocker, Thread *waiting) +{ + for (unsigned int i = 0; i < promises->size(); i++) { + Promise *promise = (*promises)[i]; + ModelAction *reader = promise->get_action(); + if (reader->get_tid() != blocker->get_id()) + continue; + if (!promise->thread_is_available(waiting->get_id())) + continue; + if (promise->eliminate_thread(waiting->get_id())) { + /* Promise has failed */ + priv->failed_promise = true; + } + } +} + /** * @brief Check whether a model action is enabled. * @@ -1202,6 +1371,7 @@ bool ModelChecker::check_action_enabled(ModelAction *curr) { Thread *blocking = (Thread *)curr->get_location(); if (!blocking->is_complete()) { blocking->push_wait_list(curr); + thread_blocking_check_promises(blocking, get_thread(curr)); return false; } } @@ -1209,16 +1379,6 @@ bool ModelChecker::check_action_enabled(ModelAction *curr) { return true; } -/** - * Stores the ModelAction for the current thread action. Call this - * immediately before switching from user- to system-context to pass - * data between them. - * @param act The ModelAction created by the user-thread action - */ -void ModelChecker::set_current_action(ModelAction *act) { - priv->current_action = act; -} - /** * This is the heart of the model checker routine. It performs model-checking * actions corresponding to a given "current action." Among other processes, it @@ -1257,7 +1417,7 @@ ModelAction * ModelChecker::check_current_action(ModelAction *curr) /* Build may_read_from set for newly-created actions */ if (newly_explored && curr->is_read()) - build_reads_from_past(curr); + build_may_read_from(curr); /* Initialize work_queue with the "current action" work */ work_queue_t work_queue(1, CheckCurrWorkEntry(curr)); @@ -1274,7 +1434,7 @@ ModelAction * ModelChecker::check_current_action(ModelAction *curr) if (process_thread_action(curr)) update_all = true; - if (act->is_read() && process_read(act, second_part_of_rmw)) + if (act->is_read() && !second_part_of_rmw && process_read(act)) update = true; if (act->is_write() && process_write(act)) @@ -1305,8 +1465,14 @@ ModelAction * ModelChecker::check_current_action(ModelAction *curr) if (act->is_read()) { const ModelAction *rf = act->get_reads_from(); - if (rf != NULL && r_modification_order(act, rf)) - updated = true; + const Promise *promise = act->get_reads_from_promise(); + if (rf) { + if (r_modification_order(act, rf)) + updated = true; + } else if (promise) { + if (r_modification_order(act, promise)) + updated = true; + } } if (act->is_write()) { if (w_modification_order(act)) @@ -1336,7 +1502,7 @@ void ModelChecker::check_curr_backtracking(ModelAction *curr) if ((parnode && !parnode->backtrack_empty()) || !currnode->misc_empty() || - !currnode->read_from_empty() || + !currnode->read_from_past_empty() || !currnode->future_value_empty() || !currnode->promise_empty() || !currnode->relseq_break_empty()) { @@ -1373,14 +1539,14 @@ void ModelChecker::print_infeasibility(const char *prefix) const { char buf[100]; char *ptr = buf; - if (mo_graph->checkForRMWViolation()) - ptr += sprintf(ptr, "[RMW atomicity]"); if (mo_graph->checkForCycles()) ptr += sprintf(ptr, "[mo cycle]"); if (priv->failed_promise) ptr += sprintf(ptr, "[failed promise]"); if (priv->too_many_reads) ptr += sprintf(ptr, "[too many reads]"); + if (priv->no_valid_reads) + ptr += sprintf(ptr, "[no valid reads-from]"); if (priv->bad_synchronization) ptr += sprintf(ptr, "[bad sw ordering]"); if (promises_expired()) @@ -1408,21 +1574,11 @@ bool ModelChecker::is_feasible_prefix_ignore_relseq() const */ bool ModelChecker::is_infeasible() const { - return mo_graph->checkForRMWViolation() || is_infeasible_ignoreRMW(); -} - -/** - * Check If the current partial trace is infeasible, while ignoring - * infeasibility related to 2 RMW's reading from the same store. It does not - * check end-of-execution feasibility. - * @see ModelChecker::is_infeasible - * @return whether the current partial trace is infeasible, ignoring multiple - * RMWs reading from the same store. - * */ -bool ModelChecker::is_infeasible_ignoreRMW() const -{ - return mo_graph->checkForCycles() || priv->failed_promise || - priv->too_many_reads || priv->bad_synchronization || + return mo_graph->checkForCycles() || + priv->no_valid_reads || + priv->failed_promise || + priv->too_many_reads || + priv->bad_synchronization || promises_expired(); } @@ -1430,8 +1586,11 @@ bool ModelChecker::is_infeasible_ignoreRMW() const ModelAction * ModelChecker::process_rmw(ModelAction *act) { ModelAction *lastread = get_last_action(act->get_tid()); lastread->process_rmw(act); - if (act->is_rmw() && lastread->get_reads_from() != NULL) { - mo_graph->addRMWEdge(lastread->get_reads_from(), lastread); + if (act->is_rmw()) { + if (lastread->get_reads_from()) + mo_graph->addRMWEdge(lastread->get_reads_from(), lastread); + else + mo_graph->addRMWEdge(lastread->get_reads_from_promise(), lastread); mo_graph->commitChanges(); } return lastread; @@ -1451,7 +1610,7 @@ ModelAction * ModelChecker::process_rmw(ModelAction *act) { void ModelChecker::check_recency(ModelAction *curr, const ModelAction *rf) { if (params.maxreads != 0) { - if (curr->get_node()->get_read_from_size() <= 1) + if (curr->get_node()->get_read_from_past_size() <= 1) return; //Must make sure that execution is currently feasible... We could //accidentally clear by rolling back @@ -1484,25 +1643,21 @@ void ModelChecker::check_recency(ModelAction *curr, const ModelAction *rf) if (act->get_reads_from() != rf) return; - if (act->get_node()->get_read_from_size() <= 1) + if (act->get_node()->get_read_from_past_size() <= 1) return; } - for (int i = 0; i < curr->get_node()->get_read_from_size(); i++) { + for (int i = 0; i < curr->get_node()->get_read_from_past_size(); i++) { /* Get write */ - const ModelAction *write = curr->get_node()->get_read_from_at(i); + const ModelAction *write = curr->get_node()->get_read_from_past(i); /* Need a different write */ if (write == rf) continue; /* Test to see whether this is a feasible write to read from */ - mo_graph->startChanges(); - r_modification_order(curr, write); - bool feasiblereadfrom = !is_infeasible(); - mo_graph->rollbackChanges(); + /** NOTE: all members of read-from set should be + * feasible, so we no longer check it here **/ - if (!feasiblereadfrom) - continue; rit = ritcopy; bool feasiblewrite = true; @@ -1511,8 +1666,8 @@ void ModelChecker::check_recency(ModelAction *curr, const ModelAction *rf) for (int loop = count; loop > 0; loop--, rit++) { ModelAction *act = *rit; bool foundvalue = false; - for (int j = 0; j < act->get_node()->get_read_from_size(); j++) { - if (act->get_node()->get_read_from_at(j) == write) { + for (int j = 0; j < act->get_node()->get_read_from_past_size(); j++) { + if (act->get_node()->get_read_from_past(j) == write) { foundvalue = true; break; } @@ -1535,7 +1690,7 @@ void ModelChecker::check_recency(ModelAction *curr, const ModelAction *rf) * read. * * Basic idea is the following: Go through each other thread and find - * the lastest action that happened before our read. Two cases: + * the last action that happened before our read. Two cases: * * (1) The action is a write => that write must either occur before * the write we read from or be the write we read from. @@ -1544,10 +1699,11 @@ void ModelChecker::check_recency(ModelAction *curr, const ModelAction *rf) * must occur before the write we read from or be the same write. * * @param curr The current action. Must be a read. - * @param rf The action that curr reads from. Must be a write. + * @param rf The ModelAction or Promise that curr reads from. Must be a write. * @return True if modification order edges were added; false otherwise */ -bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf) +template +bool ModelChecker::r_modification_order(ModelAction *curr, const rf_type *rf) { std::vector *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location()); unsigned int i; @@ -1575,26 +1731,23 @@ bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf for (rit = list->rbegin(); rit != list->rend(); rit++) { ModelAction *act = *rit; - if (act->is_write() && act != rf && act != curr) { + if (act->is_write() && !act->equals(rf) && act != curr) { /* C++, Section 29.3 statement 5 */ if (curr->is_seqcst() && last_sc_fence_thread_local && *act < *last_sc_fence_thread_local) { - mo_graph->addEdge(act, rf); - added = true; + added = mo_graph->addEdge(act, rf) || added; break; } /* C++, Section 29.3 statement 4 */ else if (act->is_seqcst() && last_sc_fence_local && *act < *last_sc_fence_local) { - mo_graph->addEdge(act, rf); - added = true; + added = mo_graph->addEdge(act, rf) || added; break; } /* C++, Section 29.3 statement 6 */ else if (last_sc_fence_thread_before && *act < *last_sc_fence_thread_before) { - mo_graph->addEdge(act, rf); - added = true; + added = mo_graph->addEdge(act, rf) || added; break; } } @@ -1605,19 +1758,17 @@ bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf */ if (act->happens_before(curr) && act != curr) { if (act->is_write()) { - if (rf != act) { - mo_graph->addEdge(act, rf); - added = true; + if (!act->equals(rf)) { + added = mo_graph->addEdge(act, rf) || added; } } else { - const ModelAction *prevreadfrom = act->get_reads_from(); - //if the previous read is unresolved, keep going... - if (prevreadfrom == NULL) - continue; - - if (rf != prevreadfrom) { - mo_graph->addEdge(prevreadfrom, rf); - added = true; + const ModelAction *prevrf = act->get_reads_from(); + const Promise *prevrf_promise = act->get_reads_from_promise(); + if (prevrf) { + if (!prevrf->equals(rf)) + added = mo_graph->addEdge(prevrf, rf) || added; + } else if (!prevrf_promise->equals(rf)) { + added = mo_graph->addEdge(prevrf_promise, rf) || added; } } break; @@ -1625,71 +1776,15 @@ bool ModelChecker::r_modification_order(ModelAction *curr, const ModelAction *rf } } - return added; -} - -/** This method fixes up the modification order when we resolve a - * promises. The basic problem is that actions that occur after the - * read curr could not property add items to the modification order - * for our read. - * - * So for each thread, we find the earliest item that happens after - * the read curr. This is the item we have to fix up with additional - * constraints. If that action is write, we add a MO edge between - * the Action rf and that action. If the action is a read, we add a - * MO edge between the Action rf, and whatever the read accessed. - * - * @param curr is the read ModelAction that we are fixing up MO edges for. - * @param rf is the write ModelAction that curr reads from. - * - */ -void ModelChecker::post_r_modification_order(ModelAction *curr, const ModelAction *rf) -{ - std::vector *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location()); - unsigned int i; - ASSERT(curr->is_read()); - - /* Iterate over all threads */ - for (i = 0; i < thrd_lists->size(); i++) { - /* Iterate over actions in thread, starting from most recent */ - action_list_t *list = &(*thrd_lists)[i]; - action_list_t::reverse_iterator rit; - ModelAction *lastact = NULL; - - /* Find last action that happens after curr that is either not curr or a rmw */ - for (rit = list->rbegin(); rit != list->rend(); rit++) { - ModelAction *act = *rit; - if (curr->happens_before(act) && (curr != act || curr->is_rmw())) { - lastact = act; - } else - break; - } + /* + * All compatible, thread-exclusive promises must be ordered after any + * concrete loads from the same thread + */ + for (unsigned int i = 0; i < promises->size(); i++) + if ((*promises)[i]->is_compatible_exclusive(curr)) + added = mo_graph->addEdge(rf, (*promises)[i]) || added; - /* Include at most one act per-thread that "happens before" curr */ - if (lastact != NULL) { - if (lastact == curr) { - //Case 1: The resolved read is a RMW, and we need to make sure - //that the write portion of the RMW mod order after rf - - mo_graph->addEdge(rf, lastact); - } else if (lastact->is_read()) { - //Case 2: The resolved read is a normal read and the next - //operation is a read, and we need to make sure the value read - //is mod ordered after rf - - const ModelAction *postreadfrom = lastact->get_reads_from(); - if (postreadfrom != NULL && rf != postreadfrom) - mo_graph->addEdge(rf, postreadfrom); - } else { - //Case 3: The resolved read is a normal read and the next - //operation is a write, and we need to make sure that the - //write is mod ordered after rf - if (lastact != rf) - mo_graph->addEdge(rf, lastact); - } - break; - } - } + return added; } /** @@ -1726,8 +1821,7 @@ bool ModelChecker::w_modification_order(ModelAction *curr) so we are initialized. */ ModelAction *last_seq_cst = get_last_seq_cst_write(curr); if (last_seq_cst != NULL) { - mo_graph->addEdge(last_seq_cst, curr); - added = true; + added = mo_graph->addEdge(last_seq_cst, curr) || added; } } @@ -1770,8 +1864,7 @@ bool ModelChecker::w_modification_order(ModelAction *curr) /* C++, Section 29.3 statement 7 */ if (last_sc_fence_thread_before && act->is_write() && *act < *last_sc_fence_thread_before) { - mo_graph->addEdge(act, curr); - added = true; + added = mo_graph->addEdge(act, curr) || added; break; } @@ -1787,14 +1880,13 @@ bool ModelChecker::w_modification_order(ModelAction *curr) * readfrom(act) --mo--> act */ if (act->is_write()) - mo_graph->addEdge(act, curr); + added = mo_graph->addEdge(act, curr) || added; else if (act->is_read()) { //if previous read accessed a null, just keep going if (act->get_reads_from() == NULL) continue; - mo_graph->addEdge(act->get_reads_from(), curr); + added = mo_graph->addEdge(act->get_reads_from(), curr) || added; } - added = true; break; } else if (act->is_read() && !act->could_synchronize_with(curr) && !act->same_thread(curr)) { @@ -1811,15 +1903,24 @@ bool ModelChecker::w_modification_order(ModelAction *curr) */ if (thin_air_constraint_may_allow(curr, act)) { - if (!is_infeasible() || - (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() == act->get_reads_from() && !is_infeasible_ignoreRMW())) { + if (!is_infeasible()) futurevalues->push_back(PendingFutureValue(curr, act)); - } + else if (curr->is_rmw() && act->is_rmw() && curr->get_reads_from() && curr->get_reads_from() == act->get_reads_from()) + add_future_value(curr, act); } } } } + /* + * All compatible, thread-exclusive promises must be ordered after any + * concrete stores to the same thread, or else they can be merged with + * this store later + */ + for (unsigned int i = 0; i < promises->size(); i++) + if ((*promises)[i]->is_compatible_exclusive(curr)) + added = mo_graph->addEdge(curr, (*promises)[i]) || added; + return added; } @@ -1913,7 +2014,7 @@ bool ModelChecker::release_seq_heads(const ModelAction *rf, if (mo_graph->checkForCycles()) return false; - while (rf) { + for ( ; rf != NULL; rf = rf->get_reads_from()) { ASSERT(rf->is_write()); if (rf->is_release()) @@ -1933,8 +2034,6 @@ bool ModelChecker::release_seq_heads(const ModelAction *rf, /* acq_rel RMW is a sufficient stopping condition */ if (rf->is_acquire() && rf->is_release()) return true; /* complete */ - - rf = rf->get_reads_from(); }; if (!rf) { /* read from future: need to settle this later */ @@ -2334,44 +2433,44 @@ ClockVector * ModelChecker::get_cv(thread_id_t tid) const */ bool ModelChecker::resolve_promises(ModelAction *write) { - bool resolved = false; + bool haveResolved = false; std::vector< ModelAction *, ModelAlloc > actions_to_check; + promise_list_t mustResolve, resolved; for (unsigned int i = 0, promise_index = 0; promise_index < promises->size(); i++) { Promise *promise = (*promises)[promise_index]; if (write->get_node()->get_promise(i)) { ModelAction *read = promise->get_action(); - if (read->is_rmw()) { - mo_graph->addRMWEdge(write, read); - } read_from(read, write); - //First fix up the modification order for actions that happened - //before the read - r_modification_order(read, write); - //Next fix up the modification order for actions that happened - //after the read. - post_r_modification_order(read, write); //Make sure the promise's value matches the write's value - ASSERT(promise->get_value() == write->get_value()); - delete(promise); + ASSERT(promise->is_compatible(write)); + mo_graph->resolvePromise(promise, write, &mustResolve); + resolved.push_back(promise); promises->erase(promises->begin() + promise_index); actions_to_check.push_back(read); - resolved = true; + haveResolved = true; } else promise_index++; } + for (unsigned int i = 0; i < mustResolve.size(); i++) { + if (std::find(resolved.begin(), resolved.end(), mustResolve[i]) + == resolved.end()) + priv->failed_promise = true; + } + for (unsigned int i = 0; i < resolved.size(); i++) + delete resolved[i]; //Check whether reading these writes has made threads unable to //resolve promises for (unsigned int i = 0; i < actions_to_check.size(); i++) { - ModelAction *read=actions_to_check[i]; - mo_check_promises(read->get_tid(), write, read); + ModelAction *read = actions_to_check[i]; + mo_check_promises(read, true); } - return resolved; + return haveResolved; } /** @@ -2385,11 +2484,10 @@ void ModelChecker::compute_promises(ModelAction *curr) for (unsigned int i = 0; i < promises->size(); i++) { Promise *promise = (*promises)[i]; const ModelAction *act = promise->get_action(); + ASSERT(act->is_read()); if (!act->happens_before(curr) && - act->is_read() && !act->could_synchronize_with(curr) && - !act->same_thread(curr) && - act->get_location() == curr->get_location() && + promise->is_compatible(curr) && promise->get_value() == curr->get_value()) { curr->get_node()->set_promise(i, act->is_rmw()); } @@ -2428,71 +2526,39 @@ void ModelChecker::check_promises_thread_disabled() * @brief Checks promises in response to addition to modification order for * threads. * - * Definitions: - * - * pthread is the thread that performed the read that created the promise - * - * pread is the read that created the promise - * - * pwrite is either the first write to same location as pread by - * pthread that is sequenced after pread or the write read by the - * first read to the same location as pread by pthread that is - * sequenced after pread. - * - * 1. If tid=pthread, then we check what other threads are reachable - * through the mod order starting with pwrite. Those threads cannot - * perform a write that will resolve the promise due to modification - * order constraints. - * - * 2. If the tid is not pthread, we check whether pwrite can reach the - * action write through the modification order. If so, that thread - * cannot perform a future write that will resolve the promise due to - * modificatin order constraints. - * - * @param tid The thread that either read from the model action write, or - * actually did the model action write. + * We test whether threads are still available for satisfying promises after an + * addition to our modification order constraints. Those that are unavailable + * are "eliminated". Once all threads are eliminated from satisfying a promise, + * that promise has failed. * - * @param write The ModelAction representing the relevant write. - * @param read The ModelAction that reads a promised write, or NULL otherwise. + * @param act The ModelAction which updated the modification order + * @param is_read_check Should be true if act is a read and we must check for + * updates to the store from which it read (there is a distinction here for + * RMW's, which are both a load and a store) */ -void ModelChecker::mo_check_promises(thread_id_t tid, const ModelAction *write, const ModelAction *read) +void ModelChecker::mo_check_promises(const ModelAction *act, bool is_read_check) { - void *location = write->get_location(); + const ModelAction *write = is_read_check ? act->get_reads_from() : act; + for (unsigned int i = 0; i < promises->size(); i++) { Promise *promise = (*promises)[i]; - const ModelAction *act = promise->get_action(); + const ModelAction *pread = promise->get_action(); // Is this promise on the same location? - if (act->get_location() != location) + if (!pread->same_var(write)) continue; - // same thread as the promise - if (act->get_tid() == tid) { - // make sure that the reader of this write happens after the promise - if ((read == NULL) || (promise->get_action()->happens_before(read))) { - // do we have a pwrite for the promise, if not, set it - if (promise->get_write() == NULL) { - promise->set_write(write); - // The pwrite cannot happen before the promise - if (write->happens_before(act) && (write != act)) { - priv->failed_promise = true; - return; - } - } - - if (mo_graph->checkPromise(write, promise)) { - priv->failed_promise = true; - return; - } - } + if (pread->happens_before(act) && mo_graph->checkPromise(write, promise)) { + priv->failed_promise = true; + return; } // Don't do any lookups twice for the same thread - if (!promise->thread_is_available(tid)) + if (!promise->thread_is_available(act->get_tid())) continue; - if (promise->get_write() && mo_graph->checkReachable(promise->get_write(), write)) { - if (promise->eliminate_thread(tid)) { + if (mo_graph->checkReachable(promise, write)) { + if (mo_graph->checkPromise(write, promise)) { priv->failed_promise = true; return; } @@ -2525,12 +2591,12 @@ void ModelChecker::compute_relseq_breakwrites(ModelAction *curr) /** * Build up an initial set of all past writes that this 'read' action may read - * from. This set is determined by the clock vector's "happens before" - * relationship. + * from, as well as any previously-observed future values that must still be valid. + * * @param curr is the current ModelAction that we are exploring; it must be a * 'read' operation. */ -void ModelChecker::build_reads_from_past(ModelAction *curr) +void ModelChecker::build_may_read_from(ModelAction *curr) { std::vector *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location()); unsigned int i; @@ -2561,8 +2627,14 @@ void ModelChecker::build_reads_from_past(ModelAction *curr) else if (curr->get_sleep_flag() && !curr->is_seqcst() && !sleep_can_read_from(curr, act)) allow_read = false; - if (allow_read) - curr->get_node()->add_read_from(act); + if (allow_read) { + /* Only add feasible reads */ + mo_graph->startChanges(); + r_modification_order(curr, act); + if (!is_infeasible()) + curr->get_node()->add_read_from_past(act); + mo_graph->rollbackChanges(); + } /* Include at most one act per-thread that "happens before" curr */ if (act->happens_before(curr)) @@ -2570,18 +2642,40 @@ void ModelChecker::build_reads_from_past(ModelAction *curr) } } + /* Inherit existing, promised future values */ + for (i = 0; i < promises->size(); i++) { + const Promise *promise = (*promises)[i]; + const ModelAction *promise_read = promise->get_action(); + if (promise_read->same_var(curr)) { + /* Only add feasible future-values */ + mo_graph->startChanges(); + r_modification_order(curr, promise); + if (!is_infeasible()) { + const struct future_value fv = promise->get_fv(); + curr->get_node()->add_future_value(fv); + } + mo_graph->rollbackChanges(); + } + } + + /* We may find no valid may-read-from only if the execution is doomed */ + if (!curr->get_node()->get_read_from_past_size() && curr->get_node()->future_value_empty()) { + priv->no_valid_reads = true; + set_assert(); + } + if (DBG_ENABLED()) { model_print("Reached read action:\n"); curr->print(); - model_print("Printing may_read_from\n"); - curr->get_node()->print_may_read_from(); - model_print("End printing may_read_from\n"); + model_print("Printing read_from_past\n"); + curr->get_node()->print_read_from_past(); + model_print("End printing read_from_past\n"); } } bool ModelChecker::sleep_can_read_from(ModelAction *curr, const ModelAction *write) { - while (true) { + for ( ; write != NULL; write = write->get_reads_from()) { /* UNINIT actions don't have a Node, and they never sleep */ if (write->is_uninitialized()) return true; @@ -2590,13 +2684,10 @@ bool ModelChecker::sleep_can_read_from(ModelAction *curr, const ModelAction *wri bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET; if (write->is_release() && thread_sleep) return true; - if (!write->is_rmw()) { + if (!write->is_rmw()) return false; - } - if (write->get_reads_from() == NULL) - return true; - write = write->get_reads_from(); } + return true; } /** @@ -2641,7 +2732,7 @@ void ModelChecker::dumpGraph(char *filename) const for (action_list_t::iterator it = action_trace->begin(); it != action_trace->end(); it++) { ModelAction *action = *it; if (action->is_read()) { - fprintf(file, "N%u [label=\"%u, T%u\"];\n", action->get_seq_number(), action->get_seq_number(), action->get_tid()); + fprintf(file, "N%u [label=\"N%u, T%u\"];\n", action->get_seq_number(), action->get_seq_number(), action->get_tid()); if (action->get_reads_from() != NULL) fprintf(file, "N%u -> N%u[label=\"rf\", color=red];\n", action->get_seq_number(), action->get_reads_from()->get_seq_number()); } @@ -2661,7 +2752,6 @@ void ModelChecker::dumpGraph(char *filename) const void ModelChecker::print_summary() const { #if SUPPORT_MOD_ORDER_DUMP - scheduler->print(); char buffername[100]; sprintf(buffername, "exec%04u", stats.num_total); mo_graph->dumpGraphToFile(buffername); @@ -2738,6 +2828,19 @@ bool ModelChecker::is_enabled(thread_id_t tid) const return scheduler->is_enabled(tid); } +/** + * Switch from a model-checker context to a user-thread context. This is the + * complement of ModelChecker::switch_to_master and must be called from the + * model-checker context + * + * @param thread The user-thread to switch to + */ +void ModelChecker::switch_from_master(Thread *thread) +{ + scheduler->set_current_thread(thread); + Thread::swap(&system_context, thread); +} + /** * Switch from a user-context to the "master thread" context (a.k.a. system * context). This switch is made with the intention of exploring a particular @@ -2753,8 +2856,8 @@ uint64_t ModelChecker::switch_to_master(ModelAction *act) { DBG(); Thread *old = thread_current(); - set_current_action(act); - old->set_state(THREAD_READY); + ASSERT(!old->get_pending()); + old->set_pending(act); if (Thread::swap(old, &system_context) < 0) { perror("swap threads"); exit(EXIT_FAILURE); @@ -2765,13 +2868,11 @@ uint64_t ModelChecker::switch_to_master(ModelAction *act) /** * Takes the next step in the execution, if possible. * @param curr The current step to take - * @return Returns true (success) if a step was taken and false otherwise. + * @return Returns the next Thread to run, if any; NULL if this execution + * should terminate */ -bool ModelChecker::take_step(ModelAction *curr) +Thread * ModelChecker::take_step(ModelAction *curr) { - if (has_asserted()) - return false; - Thread *curr_thrd = get_thread(curr); ASSERT(curr_thrd->get_state() == THREAD_READY); @@ -2779,61 +2880,24 @@ bool ModelChecker::take_step(ModelAction *curr) /* Infeasible -> don't take any more steps */ if (is_infeasible()) - return false; + return NULL; else if (isfeasibleprefix() && have_bug_reports()) { set_assert(); - return false; + return NULL; } - if (params.bound != 0) - if (priv->used_sequence_numbers > params.bound) - return false; + if (params.bound != 0 && priv->used_sequence_numbers > params.bound) + return NULL; if (curr_thrd->is_blocked() || curr_thrd->is_complete()) scheduler->remove_thread(curr_thrd); Thread *next_thrd = get_next_thread(curr); - next_thrd = scheduler->next_thread(next_thrd); DEBUG("(%d, %d)\n", curr_thrd ? id_to_int(curr_thrd->get_id()) : -1, next_thrd ? id_to_int(next_thrd->get_id()) : -1); - /* - * Launch end-of-execution release sequence fixups only when there are: - * - * (1) no more user threads to run (or when execution replay chooses - * the 'model_thread') - * (2) pending release sequences - * (3) pending assertions (i.e., data races) - * (4) no pending promises - */ - if (!pending_rel_seqs->empty() && (!next_thrd || next_thrd->is_model_thread()) && - is_feasible_prefix_ignore_relseq() && !unrealizedraces.empty()) { - model_print("*** WARNING: release sequence fixup action (%zu pending release seuqences) ***\n", - pending_rel_seqs->size()); - ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ, - std::memory_order_seq_cst, NULL, VALUE_NONE, - model_thread); - set_current_action(fixup); - return true; - } - - /* next_thrd == NULL -> don't take any more steps */ - if (!next_thrd) - return false; - - next_thrd->set_state(THREAD_RUNNING); - - if (next_thrd->get_pending() != NULL) { - /* restart a pending action */ - set_current_action(next_thrd->get_pending()); - next_thrd->set_pending(NULL); - next_thrd->set_state(THREAD_READY); - return true; - } - - /* Return false only if swap fails with an error */ - return (Thread::swap(&system_context, next_thrd) == 0); + return next_thrd; } /** Wrapper to run the user's main function, with appropriate arguments */ @@ -2847,17 +2911,57 @@ void ModelChecker::run() { do { thrd_t user_thread; - Thread *t = new Thread(&user_thread, &user_main_wrapper, NULL); - + Thread *t = new Thread(&user_thread, &user_main_wrapper, NULL, NULL); add_thread(t); - /* Run user thread up to its first action */ - scheduler->next_thread(t); - Thread::swap(&system_context, t); + do { + /* + * Stash next pending action(s) for thread(s). There + * should only need to stash one thread's action--the + * thread which just took a step--plus the first step + * for any newly-created thread + */ + for (unsigned int i = 0; i < get_num_threads(); i++) { + thread_id_t tid = int_to_id(i); + Thread *thr = get_thread(tid); + if (!thr->is_model_thread() && !thr->is_complete() && !thr->get_pending()) { + switch_from_master(thr); + } + } + + /* Catch assertions from prior take_step or from + * between-ModelAction bugs (e.g., data races) */ + if (has_asserted()) + break; + + /* Consume the next action for a Thread */ + ModelAction *curr = t->get_pending(); + t->set_pending(NULL); + t = take_step(curr); + } while (t && !t->is_model_thread()); - /* Wait for all threads to complete */ - while (take_step(priv->current_action)); + /* + * Launch end-of-execution release sequence fixups only when + * the execution is otherwise feasible AND there are: + * + * (1) pending release sequences + * (2) pending assertions that could be invalidated by a change + * in clock vectors (i.e., data races) + * (3) no pending promises + */ + while (!pending_rel_seqs->empty() && + is_feasible_prefix_ignore_relseq() && + !unrealizedraces.empty()) { + model_print("*** WARNING: release sequence fixup action " + "(%zu pending release seuqence(s)) ***\n", + pending_rel_seqs->size()); + ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ, + std::memory_order_seq_cst, NULL, VALUE_NONE, + model_thread); + take_step(fixup); + }; } while (next_execution()); + model_print("******* Model-checking complete: *******\n"); print_stats(); }